The present invention relates to methods and apparatus for examining subjects for particular physiological conditions using acoustic information. The invention is particularly useful in known techniques which utilize sounds generated by the subject and sensed at a predefined distance from the site of sound generation of the subject's body, e.g., one meter, and is therefore described below with respect to such techniques.
The measurement of the acoustic characteristics of certain body functions, particularly those related to breathing, or cessation of breathing, or partial cessation of breathing provides valuable medical information. Cases in point include, but are not limited to, the measurement of snoring intensity, which is an important medical parameter particularly in the domain of sleep medicine. Other examples related to the respiratory system include the intensity of wheezing, stridor, (high-pitched sounds), coughing, respiratory rates, etc., which are clinically important in diagnosing various respiratory system conditions. In addition, sounds related to the cardiovascular system, such a the well known ‘heart sounds’, sounds related to the musculo-skeletal system, sounds related to the gastro-intestinal system, and sounds related to specific measurement methods, such as blood pressure measurements, are also clinically important.
Measurement of the intensity of snoring is important in providing an index of the state of a patient's respiratory activity and the state of the airways during sleep. It is affected by, among other physiological factors, the degree of patency of a patient's airways, the upper airway muscle tone, mucosal swelling, and the degree of respiratory drive particularly during sleep. Measurement of the frequency spectrum of snoring sounds may also provide useful clinical information, for example, in determining the main site of the snores origin in the subject's respiratory system.
Quantitative calibration of such acoustic activity is essential for enabling the medical practitioner to gage the clinical significance of, for example, a subject's snoring activity, as a part of the diagnostic process. Traditionally, the intensity of snoring sounds has been determined as the decibel level of such sounds at some predefined distance, commonly one meter from the site of sound generation. Established clinical criteria for quantifying snoring intensity are defined in this manner.
In clinical laboratory based medicine, and in particular in the sleep medicine clinic setting, the recording of a subject's acoustic activity is traditionally performed by placing a sound level recorder, such as a microphone, at a predefined distance (e.g., one meter) from the subject. The setting up of such an acoustic measurement environment calls for considerable technical expertise and is thus clearly not suitable for performing measurements outside the confines of specialized laboratories. It is also highly susceptible to environmental acoustic activity, such as other snoring bed partners, audio devices etc., which may seriously confound the accurate measurement of a given subject's breathing activity.
In practice, measurements outside the specialist laboratory are being increasingly applied. In particular, these include ambulatory measurement systems which assume an important role in clinical medicine, and are particularly valuable in sleep medicine. The advantages of ambulatory testing are numerous and well known, and include increased patient comfort, accessibility, as well as considerable cost saving.
A major advantage, among others, in recording respiratory sound activity directly from the subject's body surface is that it considerably reduces the problem of acoustic crosstalk due to environmental noise activity, which problem is inherent to sound level measurement at a fixed distance from the subject.
The acoustic quality associated with various physiological systems may also be influenced by the movement of the body at the examination site, and also the position, posture or orientation, with respect to gravity, of the body at the examination site. Moreover, diagnosing many physiological conditions utilize not only acoustic information, but also such position and/or motion information.
The determination of multiple physiological signals, including body position, body movement and acoustic measurements related to physiological processes of the body, have been involved in a number of patent publications, including U.S. Pat. Nos. 4,784,162, 5,275,159, 6,171,258 and U.S. Patent Application 2005/0113646 A1. In these prior patent applications the measurements of body position, body movement and/or acoustic activity, was generally achieved by using separate sensors on the body surface. These sensors were not designed to enable measurement from a single common location, nor were they configured to permit them to be arranged in such a way as to facilitate measurement from a single location.
Other patent publications relative to this field are U.S. Pat. Nos. 6,468,234, 7,077,810, and International PCT Application of International Publication No. WO2005/120167. However, the developments described therein do not use acoustical or sound sensors, but rather vibration sensors sensing vibrations of the subject's body.
There are several reasons why obtaining information concerning the body position, body movement and acoustic measurements from a common site wherein the means for obtaining this information are housed within a common housing is beneficial to the assessment of a variety of physiological and pathological conditions, as illustrated by the following examples:
Application for Respiratory System
The occurrence of upper-airway increased resistance, or even complete collapse, is a hallmark of the well known obstructive sleep apnea (OSA) syndrome. An obstructive event in a patient with OSA is usually preceded by considerable acoustic activity or snoring, however this ceases when the flow of air is sufficiently attenuated due to the progression of airway narrowing.
The disappearance of snoring may, on the other hand, merely be due to a reversal of the partial airway obstruction which caused the snoring. Distinguishing between these two extreme situations may be facilitated by measuring surface motion at the measurement site. In the case of the worsening obstruction, increased surface motion which is sub-acoustic in nature is likely to be present by ongoing vibration of the tissues due to large pressure perturbations at the site of obstruction brought about by ineffectual breathing effort. An appropriate motion sensor will enable this to be sensed.
Although there are a number of locations on the body surface that may be appropriate for recording acoustic, and/or vibratory activity associated with snoring and sleep disordered breathing conditions, we have found that the best site for such measurements is the extra thoracic region extending from the chin to the sternum, and the thoracic region surrounding the supra-sternal notch. At these sites the sound and surface motion signals are best recorded due to close proximity to the source of the perturbations, and due to there being mainly soft tissues between the body surface and the airway lumen.
In order to effectively measure these multiple parameters from this region, it is highly desirable to obtain the full set of body position, body movement and acoustic information measurements from a single location. The present invention specifically addresses this objective.
Application for Blood Pressure Measurements
There are a number of well known methods for performing non-invasive blood pressure measurements. Two of the most common are the so called “Auscultatory” method and the “oscillometric” method, respectively.
In the ausculatory method, acoustic information detected by stethoscope, associated with varying degrees of arterial opening during the progressive deflation of the blood pressure cuff, are sensed, and according to the quality of the associated sound, the respective systolic and diastolic pressure values may be determined. This is the most commonly used method in clinical practice, and the so “Korotkoff” sounds are used to define the blood pressure values. Automatic devices which analyze the acoustic information are also available.
The second commonly used blood pressure measurement method is the so called “oscillometric” method, which is based on detecting fluctuations in the volume of the measured limb segment associated with varying degrees of arterial opening during the progressive deflation of the blood pressure cuff. According to the amplitude of the associated volume changes, the respective systolic, mean and derived diastolic pressure values may be determined. Sensing of the volume change is usually based on pressure change in the cuff or the magnitude of the skin motion in the vicinity of the measured artery.
In both of the above methods, the inventive device of the current application would have distinct advantages over either method alone since it would be able to provide the source information needed for the determination of BP according to both methods.
Furthermore, the addition of a body position detecting means in, for example, the traditional measurement of BP from brachial artery of the arm, would provide important information regarding the orientation of the measurement site, which could for instance be used to determine the hydrostatic offset of the arm in a seated patient, based on the angle of the arm with respect to the long axis of the body.
Finally, in the above application, accurate positioning of the sensor is critical to the success of the measurement since the location of the pulsating area is highly limited. Only an apparatus having all the sensors located at the exact site would provide sufficiently reliable data.
Cardiology
The application of both acoustic and surface motion sensing, as well as body position determination from a single common site, wherein the means for obtaining this information are housed within a common housing, may provide useful information about heart function, as illustrated in the following example.
The detection of heart sounds is a commonly used clinical practice which is particularly helpful in, among other things, detecting valvular heart disease conditions.
The clinical interpretation of the significance of the heart sounds may be affected by a patient's breathing. For example, in the so called second heart sound (which, is caused by reverberations within the blood and surrounding tissues associated with the sudden blocking of retrograde blood flow due to closure of the aortic valve and pulmonary valve respectively at the end of ventricular systole), knowledge of the patient's breathing can enable a diagnosis to be made by helping to determine if the “splitting” of the heart sound is pathological or physiological in nature.
In essence, this is related to the effect of intra-thoracic pressure on blood return into the right side of the heart. During inspiration, greater negative intra-thoracic pressure is generated which increases the blood volume in the right ventricle. This prolongs the time that the pulmonary valve stays open relative to the aortic valve.
This situation thus results in a physiological “splitting” of the second heart sound.
If however, this splitting does not vary with inspiration, it may represent a pathological state, possibly due to a left-to-right shunt of blood within the heart itself. This raises the concern of an atrial or ventricular septal defect.
Certain clinical interventions can be performed to increase the venous return to the right side of the heart, including the adoption of a supine posture, which can enhance the above described diagnosis.
In the above described example, a combined body position, body movement, and acoustic measurements apparatus would be very useful since it would facilitate the accurate recording of the heart sounds via the acoustic sensing means, the breathing pattern via the combination of body position and body movement signals, and the patients posture by the body position sensor, when it is appropriately placed on the patient's chest wall.
In addition, vibrations related to the mechanical perturbations associated with heart valve closure, and pathological conditions thereof, which are sub-acoustic in nature, may be present at the signal measurement site. An appropriate motion sensor will enable this to be sensed.
As was the case in the previously cited examples, here too, accurate positioning of the sensor is critical to the success of the measurement since the location at which heart sounds, and particularly splitting of the second heart sound area, is highly limited. Only an apparatus having all the sensors located at the exact site would provide sufficiently reliable data.
Rheumatology
The combined body position, body movement, and acoustic measurements apparatus may also be useful for quantitatively detecting and analyzing joint disorders by measuring joint movements related to sound patterns.
Since the apparatus can be used to provide a limb's position in 3D space over time, and can be used to characterize the dynamics the limb movements, the associated sound information may therefore provide a quantitative assessment of the degree of joint damage. As was the case in the previously cited examples, here too, accurate positioning of the sensor is critical to the success of the measurement. Clearly, given the limited space available for placing the apparatus at the joint location, only an apparatus having all the sensors located at the exact site would enable the measurements to be properly made to provide sufficiently reliable data.
Gastroenterology
The evaluation of several physiological processes related to the gastrointestinal system may be beneficially performed by using a combined body position, body movement, and acoustic measurements apparatus and the appropriate signal analysis. Such processes as swallowing (deglutition), peristalsis, bowel sounds, bowel transit time, may be thus analyzed. Furthermore, the use of multiple units may be beneficially applied at appropriate body sites to facilitate the evaluation. For example, applying multiple units on the surface of the abdomen overlying the intestines may be useful in determining the bowel transit time and the kinetics of bowel action and its disorders. Likewise, when applied to the throat/neck and thorax regions such units may be useful in evaluating swallowing and related disorders.